U.S. patent application number 14/390320 was filed with the patent office on 2015-02-26 for filter cleaning.
The applicant listed for this patent is SEA-LIX AS. Invention is credited to Aage Bjorn Andersen, Jason Dale.
Application Number | 20150053628 14/390320 |
Document ID | / |
Family ID | 46160295 |
Filed Date | 2015-02-26 |
United States Patent
Application |
20150053628 |
Kind Code |
A1 |
Dale; Jason ; et
al. |
February 26, 2015 |
FILTER CLEANING
Abstract
A cleaning head for a filter backwashing mechanism, the cleaning
head comprising: a nozzle for contact with a filter element wall 1
and for receiving a flow of backwash fluid 8, 9, wherein the nozzle
comprises a rotor 3 for generating a torque when exposed to the
flow of backwash fluid 8,9, and wherein the cleaning head is
arranged such that at least a part of the nozzle will move toward
and/or apply a force to the filter element wall 1 as a result of
the torque generated by the rotor 3.
Inventors: |
Dale; Jason; (Chester,
GB) ; Andersen; Aage Bjorn; (Raelingen, NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEA-LIX AS |
R.ae butted.lingen |
|
NO |
|
|
Family ID: |
46160295 |
Appl. No.: |
14/390320 |
Filed: |
April 4, 2013 |
PCT Filed: |
April 4, 2013 |
PCT NO: |
PCT/EP2013/057136 |
371 Date: |
October 2, 2014 |
Current U.S.
Class: |
210/798 ;
210/411 |
Current CPC
Class: |
B01D 29/68 20130101;
B08B 7/02 20130101; B01D 46/42 20130101; B08B 5/04 20130101; B01D
46/0068 20130101 |
Class at
Publication: |
210/798 ;
210/411 |
International
Class: |
B01D 29/68 20060101
B01D029/68 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2012 |
GB |
1206003.4 |
Claims
1. A cleaning head for a filter backwashing mechanism, the cleaning
head comprising: a nozzle for contact with a filter element wall
and for receiving a flow of backwash fluid, wherein the nozzle
comprises a rotor for generating a torque when exposed to the flow
of backwash fluid, and wherein the cleaning head is arranged such
that at least a part of the nozzle will move toward and/or apply a
force to the filter element wall as a result of the torque
generated by the rotor.
2. A cleaning head as claimed in claim 1, wherein the torque
generated by the rotor produces a linear movement of the nozzle or
part of the nozzle in a direction that is toward the filter element
wall, in use, and/or results in a linear force applied by the
nozzle or part thereof in a direction that is toward the filter
element wall, in use.
3. A cleaning head as claimed in claim 1 or 2, wherein the torque
generated by the rotor is converted into a linear force and/or
movement by a screw thread arrangement.
4. A cleaning head as claimed in claim 1, 2 or 3, wherein the rotor
is mounted to the cleaning head via a screw thread arrangement and
the screw thread has an axis of rotation that is generally
perpendicular to the surface of the filter element wall.
5. A cleaning head as claimed in claim 4, wherein the rotor forms
at least an end part of the nozzle, so that an inlet of the rotor
forms a contact part of the nozzle that is intended to contact with
the filter element wall during backwashing.
6. A cleaning head as claimed in claim 1, 2 or 3, wherein the
nozzle comprises the rotor and a separate contact part arranged for
linear movement driven by rotation of the rotor, the contact part
being for contact with the filter element wall during
backwashing.
7. A cleaning head as claimed in claim 6, wherein the rotor is
mounted to the cleaning head for rotating movement only and the
contact part is a threaded part slidably mounted with respect to a
main body of the nozzle and connected to a threaded part that
rotates driven by rotation of the rotor.
8. A cleaning head as claimed in any preceding claim comprising a
hollow conduit for passage of backwash fluid from the nozzle to
downstream parts of the backwashing mechanism, wherein the hollow
conduit supports the nozzle and/or rotor.
9. A cleaning head as claimed in claim 8, wherein the hollow
conduit comprises a joint or interface for fitting to a conduit of
an existing backwashing mechanism.
10. A cleaning head as claimed in claim 8 wherein the hollow
conduit includes a part of a main flow path for the backwashing
mechanism and a branch extending from the part of the main flow
path for supporting the nozzle.
11. A cleaning head as claimed in claim 10 wherein the part of the
main flow path comprises a segment arranged to be joined to another
similar segment of a similar hollow conduit.
12. A cleaning head as claimed in any preceding claim, wherein the
rotor comprises one or more helical rotor blade(s) with a pitch
that decreases in the direction of flow of backwash fluid.
13. A cleaning head as claimed in any preceding claim, wherein the
rotor has a conic shape, with blades formed between two conic
surfaces.
14. A cleaning head as claimed in any preceding claim, wherein the
nozzle is formed by the rotor and an outer housing or cowling of
the rotor that moves with the rotor.
15. A cleaning head as claimed in any preceding claim, wherein the
rotor comprises: at least one blade arranged to rotate about an
axis of rotation, the blade being formed by a surface extending
between inner and outer conic helixes; an inner surface and an
outer rim enclosing the blade, the inner and outer surfaces
following inner and outer generally conical surfaces of revolution
corresponding to the paths of the conic helixes, wherein the conic
helixes each have a pitch that decreases as the radius of the helix
increases and wherein the blade extends between the outer rim and
the inner surface and is mounted to at least one of the outer rim
and the inner surface, and wherein the rotor is arranged with the
small diameter end of the conic shape forming an inlet for flow of
backwashing fluid.
16. A cleaning head as claimed in claim 15, wherein the blade is
mounted to both of the outer rim and inner surface.
17. A cleaning head as claimed in claim 15 or 16, wherein the rotor
has an inlet opening at the small diameter end of the rotor that is
arranged for axial flow of fluid.
18. A cleaning head as claimed in any preceding claim, comprising a
tension or torsion spring within the filter cleaning head that
causes a `retractable` force to act on the contact part and/or on
the rotor causing the contact part to withdraw from the filter
element wall and/or causing the rotor to rotate in reverse when the
normal working load is removed.
19. A cleaning head as claimed in any of claims 1 to 17, wherein
the rotor is arranged to rotate in reverse when a reverse flow is
applied, whereby a reverse flow can be used to reverse the movement
of the contact part.
20. A backwashing mechanism comprising one or more cleaning head(s)
as claimed in any preceding claim, wherein the backwashing
mechanism is for installation in a filter with one or more filter
element(s), the filter element(s) comprising a semi-permeable
filtration wall.
21. A method of cleaning a filter element wall comprising use of a
cleaning head or backwashing mechanism as claimed in any preceding
claim for cleaning a filter element wall.
22. A method as claimed in claim 21 comprising the steps of: (A)
creating a pressure differential between outside of the filtration
screen and the filter cleaning head such that fluid is caused to
flow in a reverse direction through the filter element wall; (B)
activation of the filter cleaning head by conversion of the fluid
flow kinetic energy into sealing forces resulting in self-adjusting
sealing of the filter cleaning head with the inner wall of the
filter element thereby preventing the loss of process fluid and
increasing cleaning effectiveness; and (C) moving the filter
cleaning head relative to the filtration wall so as to remove
debris from 100% of the filtration wall.
23. A method of manufacturing a filter cleaning head comprising
providing a nozzle as described in any of claims 1 to 19.
24. A method as claimed in claim 23 being a method of manufacturing
a backwashing mechanism comprising retro-fitting the cleaning head
to a pre-existing backwashing mechanism.
25. A cleaning head substantially as hereinbefore described with
reference to the accompanying drawings.
Description
[0001] The invention relates to a filter cleaning head and to a
related method of cleaning a filter, for example for cleaning a
filter element of a water filtration device.
[0002] Filtration is a preparatory step in many fluid treatment
processes and in particular in water treatment processes. Such
processes are typically aimed at improving water quality and to
reducing risks associated with water or other liquids containing
unwanted elements. Filtering processes are also used to remove
solids and liquids from a process gas. The filtering may be to
enable effective use of the fluid in a subsequent process, for
example as a process fluid in a cleaning, cooling or manufacturing
process. Improved filtration technologies will benefit currently
applied treatment methods regardless of media and applications and
further open up for the development of improved processes and
technologies.
[0003] Filtering is conventionally used in numerous applications
such as fresh water applications, potable water production
including recirculation of water from domestic and industrial
processes, cooling-water intake for power plants, produced water
treatment applications from oil/gas exploration, sea water
applications, waste water applications and aquaculture applications
on land or on floating units such as floating aquaculture
installations (fish farms), air conditioning and gas purification,
installations associated with the production of oil and gas as well
as on-board ships, ballast water management on-board ships, food
and drink processing, mineral and slurry processing, pharmaceutical
processing, chemical processing and power generation applications
such as pre-processing of power station cooling water or processing
of electrical transformer oils. Whilst many of these uses for
filtration involve water based liquids the use of filters of the
type described herein is not limited to water based liquids alone
but could also be used to treat acids and alkalis or other fluids
where it is desirable to remove unwanted elements from the
fluid.
[0004] Many of these uses require filtration of a high volume of
water at high flow rates. An example of this is the filtration of
ship ballast water, for example during treatment of the ballast
water to kill micro-organisms, and this is of increasing importance
to ship builders and fleet operators. Transferring large volumes of
sea water between distinct geographical locations is known to be
damaging to marine biodiversity. Regulatory requirements and
environmental concerns make it important to effectively treat
ship's ballast water before it is discharged in order to remove
contaminants and organisms, including micro-organisms. Regulations
set onerous requirements for the size of organism that must be
removed or disabled and this gives rise to a need for effective
filtration and micro-filtration of large volumes of water. The
scale of modern ships means the volumes of ballast water tanks is
large and consequently the time taken to load and unload ballast
tanks is of commercial importance to fleet operators. Additionally,
space is surprisingly scarce on-board ships. As a result, efficient
filtration systems or more specifically micro-filtration systems
that are space efficient and still capable of filtering large
volumes of water and removing a considerable amount of matter
(organic as well as in-organic) are highly desirable.
[0005] A range of filter systems are available to that can filter
fluids in these applications. Such systems generally comprise a
conventional filter element through which the fluid, raw sea water,
for example, flows. All filter systems naturally require the
material that is filtered out to be removed. In a typical system,
as the liquid flow passes through the wall of the filter elements
any dirt, particles or organic matter greater in size than the
filter size specification may not pass through the filter element
and are trapped on the internal wall of the filter element and
begin to form an accretion of filter residue, known as a `cake`. As
the cake of matter builds-up the pressure loss over the filter
element increases. It is necessary for the accreted filter residue
to be cleaned off the interior wall of the filter element in order
to maintain efficiency. Even the best filter designs will suffer
from build-up of residue and this problem increases as the
effectiveness of the filter in removing solids from the liquid is
increased. Thus, to provide an effective filtering of liquid it is
necessary to not only provide an improved filtration but also to
ensure effective cleaning of the filter.
[0006] This cleaning process can be achieved by stripping down the
filter to gain access to the filter elements. This has obvious
disadvantages in relation to the need for maintenance personnel,
access to the filter, and down time for the filter apparatus. A
more self-sufficient filtration mechanism can be provided by the
use of a backwashing process. Such a process uses a backwashing
mechanism that may be configured for continuous cleaning or
triggered only when the pressure loss over the filter reaches a
certain monitored level or triggered at present intervals or
manually. The pressure loss will increase as the `cake` of filter
residue builds-up. Various filter cleaning heads have been employed
in various backwashing mechanisms which allow the filter element to
be cleaned through reverse water flow through the filter wall. The
reverse flow dislodges filtered material, which can then be removed
from the filter apparatus.
[0007] WO 2006/008729 and WO 2011/058556 describe known backwashing
processes, in which a cleaning head is passed over the filter wall
to clean the filter and remove filter residue. The cleaning head
uses a local flow reversal in a relatively small part of the filter
wall to dislodge the residue and to remove it from the filtration
apparatus. This backwashing process can be performed whilst the
filter is in use thus allowing the filter to continuously filter
water whilst being cleaned. The cleaning head is arranged to move
over the filter surface so that all areas can be cleaned. Typically
the filter surface is a cylinder and the cleaning head is arranged
to move over the cylindrical surface following a helical path in
order to clean the whole surface. The cleaning head must be in
close contact with the filter surface during the cleaning operation
in order to maintain the pressure difference for reverse flow. This
means that some device is required for holding the cleaning head
against the filter surface. In addition, the contact portion of the
cleaning head will suffer wear due to sliding contact with the
filter surface. This means that it is necessary to either adjust
the device constantly or to provide some mechanism for
automatically adjusting the position to the cleaning head in order
to maintain close contact with the filter surface as the contact
portion wears away.
[0008] In WO 2006/008729 adjustment of the cleaning head position
is achieved by the use of a spring element in the cleaning head,
which pushes the cleaning head against the filter wall. However,
the spring must provide a sufficient force to hold the cleaning
head against the cleaning wall under the highest expected pressure
differential. This has the result that the cleaning head is
generally pushed too hard against the wall during normal
operational pressure differences, which can be considerably lower
than the maximum design pressure difference. The increased force
increases wear and results in undesirable deformation of and damage
to the filter wall.
[0009] WO 2011/058556 attempts to improve the device of WO
2006/008729 by the use of a resilient bellows with a different
elastic deformation characteristic to the spring of WO 2006/008729.
However, the bellows arrangement creates further problems, since
when there is a high pressure differential then the suction
pressure can cause the bellows to retract. This requires an
arrangement for equalisation of pressure to ensure that the
cleaning head remains in contact with the filter wall. The pressure
equalisation uses specially introduced holes in order to equalise
pressures in and around the filter cleaning head. These holes are
prone to blockage by dirt since the holes are necessarily located
on the dirty side of the filter element.
[0010] Thus, with the spring device of WO 2006/008729 the force
applied between the cleaning head and the filter wall at low
pressure differentials is too high, whereas the bellows device of
WO 2011/058556 requires pressure equalisation to avoid loss of
contact with the filter wall at high pressure differentials.
[0011] Viewed from a first aspect, the present invention provides a
cleaning head for a filter backwashing mechanism, the cleaning head
comprising: a nozzle for contact with a filter element wall and for
receiving a flow of backwash fluid, wherein the nozzle comprises a
rotor for generating a torque when exposed to the flow of backwash
fluid, and wherein the cleaning head is arranged such that at least
a part of the nozzle will move toward and/or apply a force to the
filter element wall as a result of the torque generated by the
rotor.
[0012] With this arrangement the nozzle or a part of the nozzle can
be pushed against the filter wall by a force that is produced based
on the flow of backwash fluid. The torque generated by the rotor
will vary in accordance with the flow rate of the fluid, which
itself will vary dependent on the pressure differential. As a
consequence the force that keeps the nozzle part in contact with
the filter wall is dependent on the pressure differential. This
avoids the problems with the prior art systems described above. At
low pressure differentials a lower torque is generated and hence
the pressure applied to the wall is not excessive as in WO
2006/008729. Higher pressure differentials are matched by higher
torques and there is no need for a pressure equalisation mechanism
as in WO 2011/058556. This reduces the risk of fouling functional
parts of the cleaning head by debris.
[0013] In a preferred embodiment the torque generated by the rotor
produces a linear movement of the nozzle or a part of the nozzle in
a direction that is toward the filter element wall, in use, and/or
results in a linear force applied by the nozzle or part thereof in
a direction that is toward the filter element wall, in use. The
rotor may be mounted in any fashion with any suitable mechanism
being used to convert rotation of the rotor into a linear
motion/force. However, the rotor is preferably mounted in the
cleaning head with an axis of rotation that is generally
perpendicular to the surface of the filter element wall. The torque
generated by the rotor may be converted into a linear force and/or
movement by a screw thread arrangement.
[0014] In a preferred embodiment the rotor is mounted to the
cleaning head via a screw thread arrangement and the screw thread
has an axis of rotation that is generally perpendicular to the
surface of the filter element wall. This means that the rotor
itself will move linearly as it rotates and hence may comprise the
part of the nozzle that moves toward the filter element wall. For
example, there may be a threaded shaft directly connected to the
rotor or to the cleaning head, with the other end of the rotor or
the cleaning head being provided with a threaded hole or nut.
Preferably the thread mechanism is enclosed and sealed to prevent
fluid ingress and to thereby avoid fouling of the thread with
debris from the unfiltered process fluid. The rotor may form at
least an end part of the nozzle, so that an inlet of the rotor
forms the contact part of the nozzle that is intended to contact
with the filter element wall.
[0015] In an alternative preferred embodiment, the nozzle comprises
the rotor and a separate contact part arranged for linear movement
driven by rotation of the rotor, the contact part being for contact
with the filter element wall during backwashing. With this
arrangement, the rotor may be mounted to the cleaning head for
rotating movement only, for example via a bearing or similar. The
contact part may be a threaded part slidably mounted with respect
to a main body of the nozzle and connected to a threaded part that
rotates driven by rotation of the rotor, such as a threaded part of
the rotor itself. One particular arrangement for the contact part
may comprise a threaded rod slidably mounted along the axis of
rotation of the rotor and engaged with a complementary threaded
hole along the rotor axis, whereby rotation of the rotor moves the
contact part in a linear manner so that an end of the contact part
is pushed against the filter element wall during backwashing.
[0016] With this type of arrangement since the contact part moves
linearly without rotation then wear of the contact area is reduced
in comparison to the above arrangement where the rotating rotor
moves toward and makes contact with the filter element wall. The
trade-off is a potentially more complex mechanism since there are
at least two moving parts, these being the linearly sliding contact
part and the rotating rotor.
[0017] Preferably the rotor comprises an inlet that receives
backwash fluid and an outlet that discharges backwash fluid to
downstream parts of the backwashing mechanism.
[0018] The cleaning head may be arranged so that all of the
backwash fluid for the cleaning head passes through the rotor
before being passed to downstream parts of the backwashing
mechanism. This maximises torque production and maximising the flow
rate through the rotor also minimises fouling of the rotor and
build-up of filter residue within the rotor and associated parts of
the cleaning head.
[0019] As the contact part at the tip of the nozzle is moved over
the inner wall of the filter element in contact with the wall then
wear may take place. It is preferred that a relatively soft
material such as plastic or PTFE or a slightly deformable material
is used for the contact part of the nozzle in order to reduce
friction and reduce wear of the expensive filter element and absorb
small manufacturing tolerances. Thus, the material of the contact
part is preferably softer than the material of the filter element
wall. As wear takes place, the contact part of the nozzle will be
allowed to move further toward the filter wall propelled by the
torque from the rotor, increasing its linear movement until the tip
of the nozzle once again creates a seal between the inner wall of
the filter element and the nozzle. Therefore, the nozzle
automatically compensates for wear of the nozzle up to a
predetermined limit. Once this predetermined limit is reached the
nozzle may be easily replaced.
[0020] Preferably the filter cleaning head includes a hollow
conduit for passage of backwash fluid from the nozzle to downstream
parts of the backwashing mechanism. The hollow conduit may support
the rotor and/or nozzle, for example the hollow conduit may hold a
bearing that supports the rotor or a threaded shaft or nut that
supports a corresponding nut or threaded shaft of the rotor.
[0021] The filter cleaning head may be designed to be retro-fitted
onto an existing backwashing mechanism, for instance the hollow
conduit may comprise a joint or interface for fitting to a conduit
of an existing backwashing mechanism.
[0022] Alternatively, the filter cleaning head may be designed
together with other parts of the backwashing mechanism and
manufactured as a part of a backwashing mechanism designed for use
with this filter cleaning head. In this case one preferred
embodiment comprises a hollow conduit including a part of a main
flow path for the backwashing mechanism and a branch extending from
the part of the main flow path for supporting the nozzle. The
hollow conduit may be a T-shape. Multiple cleaning heads may hence
be connected together by joining the parts of the main flow path in
order to produce a backwashing mechanism including multiple
cleaning heads on branches extending from a common main flow
path.
[0023] The part of the main flow path preferably comprises a
segment arranged to be joined to another similar segment, for
example via two tubes interconnecting in a plug and socket fashion,
optionally with a `snap fit`. This allows a backwashing mechanism
to be made up of a plurality of filter cleaning heads spaced along
the length of any size of filter element and separated by a
predetermined distance. Plastic `hooks` and seals may be included
in the hollow conduit to facilitate the assembly and sealing of
each segment. The assembled hollow conduits then hold the plurality
of filter cleaning heads in their correct respective locations
relative to each other. The hollow conduits may be rotated relative
to one another about the axis of the main flow path so that the
branches and hence the nozzles extend away from the main flow path
in different directions. The backwashing mechanism may further
include suitable end pieces for the main flow path of the multiple
hollow conduits in order for connection to the remainder of the
backwashing mechanism.
[0024] The rotor preferably comprises one or more helical rotor
blade(s) with a pitch that decreases in the direction of flow of
backwash fluid. Thus, the blade(s) may have a pitch that is larger
at the and of the rotor closest to the filter element wall, in use,
and smaller at the other end of the rotor.
[0025] The rotor may have a conic shape, with blades formed between
two conic surfaces.
[0026] The nozzle may be formed by the rotor and an outer housing
or cowling of the rotor that moves with the rotor as it moves
linearly relative to the filter element wall.
[0027] In a preferred embodiment the rotor comprises: at least one
blade arranged to rotate about an axis of rotation, the blade being
formed by a surface extending between inner and outer conic
helixes; an inner surface and an outer rim enclosing the blade, the
inner and outer surfaces following inner and outer generally
conical surfaces of revolution corresponding to the paths of the
conic helixes, wherein the conic helixes each have a pitch that
decreases along the flow direction and wherein the blade extends
between the outer rim and the inner surface and is mounted to at
least one of the outer rim and the inner surface. The use of a
rotor as described above has been found to give an effective
mechanism for the required movement of the nozzle. In one example
arrangement the radius of the helix increases along the flow
direction and the rotor is arranged with the small diameter end of
the conic shape forming an inlet for flow of backwashing fluid.
Thus, the small diameter end of the cone faces the filter element
wall, in use, with the large diameter end of the cone forming the
outlet for backwashing fluid as it passes from the nozzle to
downstream parts of the backwashing mechanism. Alternatively, it
would be possible for the pitch to decrease with decreasing radius
so that a large diameter end of the rotor forms the inlet for
backwashing fluid.
[0028] Preferably the blade is mounted to both of the outer rim and
inner surface. This means that the outer rim is joined directly to
and rotates with the blade and the remainder of the rotor. As a
result, when the rotor moves linearly as well as rotating, there is
no need for any complicated arrangement for connection of the outer
rim or inner surface to allow movement of these parts relative to
the conduit as the rotor nozzle moves toward or away from the
filter element wall.
[0029] In the present context, a conic helix is a three dimensional
curve formed on a surface of a generally conical body. The surface
of the generally conical body may be conical, frustoconical or any
other shape formed as a surface of revolution that has a generally
increasing or decreasing radius. Thus the surface is not
specifically limited to a straight sided cone but could instead be
a convex sided cone or frustocone such as a zone or ogive nose cone
shape, or alternatively the cone could be a concave sided cone or
frustocone. What is important is that each conic helix is formed
with a radius that increases along an axis of the rotor and a pitch
that decreases as the radius increases. The inner and outer conic
helixes preferably have the same decrease in pitch, although
applications are possible where a different decrease in pitch for
the inner and outer conic helix may be used.
[0030] The terms "inner" and "outer" are used herein to refer to
portions of the rotor that are at a smaller or greater radius from
the axis of rotation of the rotor.
[0031] Internally, the rotor has one or more flow passages formed
between front and back blade surfaces, the outer rim and the inner
surface. The flow passages effectively contain the flowing fluid
and prevent energy being lost due to tip losses. When the blade
extends between and is mounted to both of the outer rim and inner
surface then the flow of fluid is fully contained and tip losses
are minimised.
[0032] In a preferred embodiment the rotor has an inlet opening at
the small diameter end of the rotor that is arranged for axial flow
of fluid, preferably for solely axial flow. Thus, the opening is
perpendicular to the axis of rotation of the rotor and the blades
are preferably formed to receive fluid flowing in a generally axial
direction and preferably without any (significant) radial flow.
Preferably the rotor has an outlet opening at the large diameter
end that is also perpendicular to the axis of rotation of the
rotor. However, in the preferred embodiment the blades at the large
diameter end are not arranged for solely axial flow, but instead
may be adapted to expel fluid flowing with a radial component to
its movement.
[0033] The inner and outer conic helixes preferably start at the
same longitudinal position along the axis of rotation of the rotor
before extending along the direction of the axis of rotation of the
rotor. Preferably the inner and outer conic helixes also extend for
about the same axial length along the direction of the axis of
rotation of the rotor. With this arrangement when an outer rim of
the rotor is present it naturally encloses an opening that requires
an axial component of the flow for fluid to flow through the
opening.
[0034] The conic helix can be any suitable shape that allows for a
three dimensional curve with a decreasing pitch and optionally an
increasing radius as described above. One preferred option is the
use of an Archimedean spiral with a linear increase in radius, can
be used to produce a rotor with a simple shape based on a straight
sided frustocone. However, the conic helix could alternatively be
based on Euler, Fibonacci, Hyperbolic, Lituus, Logarithmic,
Theodorus or any other known spiral having varying radius r as a
function of the polar coordinate .theta. but also having a third
variable, the length l, varying also as function of the polar
coordinate .theta.. Some curves and/or the use of non-linear radius
increases will result in conic helixes based on conical shapes with
convex or concave sides, as discussed above.
[0035] The inner and outer conic helix may be based on the same
form of spiral or curve, with different initial and final radii.
Alternatively, different forms of curve or spiral could be used for
the inner and outer conic helix to produce a more complex shape for
the blade.
[0036] Whilst a single blade could be used it is advantageous to
use multiple blades. This creates multiple flow passages and also
allows the rotor to be easily balanced. The choice of two, three or
more rotor blades may depend on a balance of rotor strength, ease
of manufacture and energy lost to friction. In the present
embodiment, three rotor blades is the preferred choice since it
offers a strong and balanced three point construction with minimal
friction loss.
[0037] The blade or blades are preferably formed as surfaces
generated by straight lines between points on the inner and outer
conic helixes at the same longitudinal distance along the direction
of the axis of rotation of the rotor. Thus, the blade surface may
connect the pair of conic helixes in the radial direction.
Alternatively, the blades may be formed as surfaces generated by
curves between points on the inner and outer conic helixes at the
same longitudinal distance along the direction of the axis of
rotation of the rotor. With this arrangement the blades surfaces
may, for example, be concave when viewed from the large diameter
end of the rotor.
[0038] The inner and outer conic helixes may both increase in
radius at the same rate, such that the conic surfaces are generally
parallel. However, it can be advantageous to adjust the performance
of the rotor by having a different rate of increase in diameter for
the inner and outer conic helixes. The inner conic helix may
increase in radius at a slower rate than the increase in radius of
the outer conic helix in order to reduce or restrict the
hydrodynamic reaction forces and torsional forces produced by the
rotor. Alternatively, the inner conic helix radius may increase at
a faster rate than the outer conic helix radius in order to
increase hydrodynamic reaction forces and torsional forces.
[0039] The parameters discussed above, including the radius of the
conic helix, pitch of the conic helixes and the relative increase
in radius of the inner and outer conic helixes are preferably
varied linearly along the length of the rotor. However, non-linear
variations of radius, pitch and relative radius would also be
possible.
[0040] The fluid flow kinetic energy converted by the nozzle is
fully adjustable. A desired torsional force for a predetermined
flow condition can be achieved by adjusting one or more of (A) the
rate of change of radius of one conic helix or both conic helix;
(B) the relative change of radius of inner and outer conic helix
(C) the change in pitch of one or both conic helix.
[0041] Seals or flexible stretchable covers to prevent lost process
fluid may be provided between the rotor and the hollow conduit that
the rotor is supported by. These seals may be passive O-ring or lip
type of seals or may be spring or otherwise activated depending on
the application and the level of sealing required or they may be a
flexible stretchable cover that distorts easily when the rotor
rotates.
[0042] The sealing force applied by the nozzle to the filter
element wall must be selected carefully so as to provide an
effective seal between the contact part of the nozzle and the inner
wall of the filter element but should not be selected to produce
such a high force that the nozzle creates a force that may deform
the filter element wall, create excessive wear or is not able to be
reversed by an opposing force that might be experienced in normal
operation of the backwashing mechanism. Such an opposing force may
occur if the manufacturing tolerance of the filter element requires
the nozzle to `back off` or a short distance so as to accommodate
the small differences in dimensions of the filter element.
Providing the sealing force is selected carefully, an opposing
force is able to cause a reverse rotation of the nozzle thus
minimising the chance of seizure or damage to the filter element.
Once the variation in manufacturing tolerance has passed the
contact part of the nozzle may advance in its normal way towards
the filter element wall.
[0043] When there is no backwash flow, the sealing force is zero,
then the nozzle is deactivated, and the contact part only very
lightly touches the inner wall of the filter element. Normally, at
this time the backwashing mechanism is motionless as there is no
need for the backwashing mechanism to operate. As a zero sealing
force occurs between the nozzle and the filtration wall,
dismantling of the backwashing mechanism should be easy to perform.
However, in some application is may be advantageous to include a
tension or torsion spring within the filter cleaning head that
causes a `retractable` force to act on the contact part and/or on
the rotor causing the contact part to withdraw from the filter
element wall and/or causing the rotor to rotate in reverse when the
normal working load is removed i.e. backwashing ceases. Moving the
contact part of the nozzle in a linear motion away from the
filtration wall in this way allows a clearance between the contact
part and the inner wall of the filter element. Alternatively, a
device may be provided to create a flow of fluid through the rotor
in the reverse direction to the backwash flow, hence reversing the
rotation of the rotor thereby also moving the contact part of the
nozzle in a linear motion away from the filtration wall allowing a
clearance between the contact part and the inner wall of the filter
element. Or a simpler mechanism could be to include blank holes in
the nozzle so that a suitable tool can be inserted and the contact
part can be backed off manually by hand.
[0044] Preferably the filter cleaning head forms part of a
backwashing mechanism for installation in a filter with one or more
filter element(s), the filter element(s) comprising a
semi-permeable filtration wall and a filter cleaning head forming
part of the backwashing mechanism.
[0045] The filter elements may be elements constructed by a metal
weave-wire sintered screen method where multiple metal screen
layers are sintered together with supporting structures to create a
strong filter element that is able to support its own weight.
Alternatively, other types of filter element design may be used
that under the operating conditions of the filter are permeable to
one or more selected components of the liquid mixture, solution or
suspension under treatment and is impermeable to the remaining
components. Such filter elements may be constructed from natural or
processed fibre, man-made organic or synthetic materials, ferrous
and non-ferrous metals, glass, activated or natural carbon,
ceramics, papers and plastics, sheet or woven materials, non-woven
materials, pleated meltspun materials, inorganic bonded porous
media, mineral wools, glass fibre, carbon fibre, woven wire and
screens, sintered wire mesh, perforated plate, wedge wire and
membrane type of designs or any combination thereof.
[0046] As an additional benefit, the filter element may
advantageously be coated with a suitable compound to provide
increased corrosion resistance and/or improved surface qualities.
For example, coatings prepared from e.g. T.sub.iO.sub.2 or
Polyaniline-nano-T.sub.iO.sub.2 particles synthesized by in-situ
polymerization have excellent corrosion resistance in aggressive
environments. The individual filter elements may therefore be
coated to improve corrosion resistance. In addition the
nano-surface achieved can provide improved surface qualities making
the surface very slippery and difficult for matter to `stick` to
the surface thereby requiring less frequent cleaning. The slippery
surface also reduces wear of the contact part of the nozzle.
[0047] The filtration size specification is determined according to
the liquid and particle properties to be filtered. Thus, the
filtration size (that is the size of the holes or flow paths
through the filter element) may be any suitable size depending on
the desired application. For example the filtration size
specification of the filter elements may be selected to be <1,
1, 10, 20, 40 or 50 microns or greater depending on the
application.
[0048] The backwash flow is generated by a pressure differential
across the filter element wall and this may be achieved in any
suitable way. Advantageously however the pressure differential may
be achieved by reducing the pressure at the backwashing flow outlet
that communicates with the filter cleaning head via the hollow
conduit. This consequently reduces the pressure at the inlet to the
filter cleaning head and causes debris to move into the filter
cleaning head, along the hollow conduit communicating with the
filter cleaning head and finally to the backwash outlet.
[0049] The difference between atmospheric pressure at the backwash
outlet and the pressure on the outside of the filter element may be
sufficient to achieve the required back flow and in such an
arrangement a control valve may be provided to selectively open and
close the backwash outlet thereby creating the required reverse
back flow.
[0050] Additionally, or alternatively, a vacuum or suction
apparatus may be provided to increase the pressure differential to
enhance the back-wash or cleaning operation. In such an arrangement
a vacuum or suction apparatus may be coupled to the backwash outlet
or to the hollow conduit communicating with the filter cleaning
head, either in combination with the control valve or alone.
[0051] Advantageously, in filter arrangements that incorporate a
plurality of filter elements then each filter element is provided
with a backwashing mechanism within the filter element but the
multiple filter elements may have a common backwashing outlet. With
a plurality of cylindrical filter elements the backwashing
mechanisms can be mounted with alignment to the centre line of each
filter element and can be driven independently of each other or
simultaneously or as a sub-group, for example in pairs. Thus, the
filter arrangement can be backwashed in the most effective manner
with minimal detrimental influence on process fluid flow within the
filter arrangement. Indeed, the multiple backwashing mechanisms
could also be programmed to automatically adjust depending on the
filtration load so that two, three or all of the backwashing
mechanisms operate together with the maximum efficiency possible
depending on the pressure loss detected over the filter
elements.
[0052] In order to move the backwashing mechanism the assembly may
be provided with a drive mechanism arranged to rotate the
backwashing mechanism whilst simultaneously moving the backwashing
mechanism in a linear motion along the axis of the filter element.
Movement may be by means of an electric motor and screw or other
electro-mechanical, pneumatic or hydraulic arrangement.
[0053] As the backwashing mechanism is simultaneously rotated and
moved linearly, each filter cleaning head forming part of the
backwashing mechanism follows a helical trajectory as it traverses
the filter surface. Thus, the filter cleaning head is able to be
conveyed over 100% of the entire inner surface of the filter
element such that debris can be collected from all parts of the
filter element wall. The entire surface of the filter element wall
can be cleaned of debris. The filter element can be backwashed
whilst allowing the normal operation of the filter arrangement to
continue i.e. the backwashing can take place during normal
filtration.
[0054] The backwashing mechanism preferably supports a plurality of
filter cleaning heads which may be spaced along the axial length of
the filter element and separated by a predetermined distance. In
this way, the amount of linear movement required may be divided by
the number of filter cleaning heads so that each filter cleaning
head need only be conveyed over part of the inner surface of the
semi-permeable wall of the filter element whilst still reaching and
cleaning 100% of the semi-permeable filtration wall.
[0055] Advantageously, the filter cleaning head forming part of the
backwashing mechanism is scalable up to very high filtration
capacities from less than 100 m.sup.3/hr to above 10,000 m.sup.3/hr
by simply duplicating the filter cleaning heads, in line with the
area of the filter element to be cleaned.
[0056] The filter cleaning head ultimately provides an improved
overall backwashing mechanism which efficiently and effectively
removes debris from the filtration wall of each filter element. The
rotor arrangement advantageously converts fluid flow kinetic energy
in the backwash flow into a sealing force that results in the close
alignment of the filter cleaning head with the inner wall of each
filter element. This enables an improved sealing effect resulting
in a highly efficient cleaning of the filtration wall with minimal
process fluid loss.
[0057] The geometry of the nozzle, rotor and the hollow conduit
that it rotates within and is supported by lends itself well to
efficient manufacture and assembly. These parts may be made from
machined, cast or welded material but preferably they may be
injection moulded or made by rapid prototyping methods to reduce
the costs of mass production.
[0058] The inclusion of the filter cleaning head herein forming
part of the backwashing mechanism improves the overall efficiency
of the backwashing mechanism. The process fluid loss through the
improved backwashing mechanism compared with prior art is reduced.
Additionally, the cleaning of the filter is also improved. These
improvements allow for a reduction of filter mesh sizes without
reducing the flow-rate or capacity of a given filter arrangement.
Thus, the improved cleaning allows for improvements to the
filtration process. Liquid can be subsequently delivered to a (high
capacity) treatment process which is considerably "cleaner" because
of finer filtration, and this will reduce the burden on the
treatment process allowing it to be scaled down (e.g. reducing the
concentration of "conditioning" chemicals or opening up for
introducing alternative treatment processes).
[0059] It will be recognised that the cleaning head may be utilised
not only for liquid filtering but also in gas filtration
arrangements. For example the cleaning head may be used in a filter
that filters solid particles from a gas stream.
[0060] Viewed from a second aspect, the invention provides a method
comprising use of a cleaning head for cleaning a filter element
wall, wherein the cleaning head is as described in relation to the
first aspect above, and optionally as described in relation to
preferred features of the first aspect. The method may comprise use
of a backwashing mechanism as discussed above.
[0061] The method may comprise the steps of: (A) creating a
pressure differential between outside of the filtration screen and
the filter cleaning head such that fluid is caused to flow in a
reverse direction through the filter element wall; and (B)
activation of the filter cleaning head by conversion of the fluid
flow kinetic energy into sealing forces resulting in self-adjusting
sealing of the filter cleaning head with the inner wall of the
filter element thereby preventing the loss of process fluid and
increasing cleaning effectiveness; and (C) moving the filter
cleaning head(s) relative to the filtration wall so as to remove
debris from 100% of the filtration wall.
[0062] Thus, according to such an aspect there is provided for a
method of efficiently and effectively backwashing a filter
arrangement.
[0063] Viewed from a third aspect, the invention provides a method
of manufacturing a filter cleaning head comprising providing a
nozzle as described in relation to the first aspect above, and
optionally as described in relation to preferred features of the
first aspect. The method may be a method of manufacturing a
backwashing mechanism and may advantageously include retro-fitting
the cleaning head to a pre-existing backwashing mechanism, or
alternatively providing part or all of the entire cleaning heads in
a backwashing mechanism.
[0064] Certain preferred embodiments of the invention will now be
described by way of example only and with reference to the
accompanying drawings in which:
[0065] FIGS. 1a and 1b illustrate a filter cleaning head and its
various components in cross-section;
[0066] FIGS. 1c and 1d illustrate an alternative filter cleaning
head in cross-section;
[0067] FIG. 2 shows a cross-section of a filter cleaning head that
is able to be retro fitted onto an existing backwashing
mechanism;
[0068] FIG. 3a is a cross-section of a modular conduit segment for
holding the filter cleaning head;
[0069] FIG. 3b shows two conduit sections joined together forming a
part of a backwashing mechanism for a cylindrical filter
element;
[0070] FIG. 4 shows a filter with a single filter element having a
backwashing mechanism with multiple filter cleaning heads;
[0071] FIG. 5 shows a filter with multiple similar filter elements,
each filter element having a backwashing mechanism with multiple
filter cleaning heads;
[0072] FIGS. 6a and 6b show an embodiment of a rotor in side view
and end view,
[0073] FIGS. 7a and 7a show the rotor of FIG. 6 with the outer
peripheral rim partially cut-away so that more detail of the rotor
design is visible,
[0074] FIGS. 8a and 8b are perspective views of the rotor of FIGS.
6 and 7 with the outer rim partially and fully omitted,
[0075] FIGS. 9a and 9b show an alternative embodiment of a rotor
where the inner conic helix radius increases at a lesser rate than
the outer conic helix radius,
[0076] FIGS. 10a and 10b show a further alternative where the inner
conic helix radius increases at a greater rate than the outer conic
helix radius.
[0077] FIGS. 11a and 11b show an alternative embodiment where the
helical pitch is decreased at a lesser rate than the rotor of FIGS.
6 and 7,
[0078] FIGS. 12a and 12b show an alternative embodiment where the
helical pitch is decreased at a greater rate than the rotor of
FIGS. 6 and 7.
[0079] FIG. 13 is a graph showing the variation in torsional forces
generated by a rotor as the ratio of the minimum radius do and
maximum radius Do of the conic helix is changed,
[0080] FIG. 14 is a graph showing the variation in torsional forces
generated by a rotor with modification to the rate at which the
inner conic helix radius increases compared to the outer conic
helix radius, and
[0081] FIG. 15 is a graph showing the variation in torsional forces
generated by a rotor when the rate of decrease of the helical pitch
is adjusted by altering the rate of increase of helical
frequency.
[0082] FIGS. 1a and 1b illustrate a first embodiment of the filter
cleaning head and its various components. The filter cleaning head
element in FIGS. 1a and 1b is applied to a semi-permeable filter
element wall 1, which in the preferred embodiment is a metal
weave-wire sintered screen. A hollow conduit 2 connects a combined
rotor/nozzle 3 to the remainder of the backwashing mechanism and
also acts to support the rotor/nozzle 3. The rotor/nozzle 3 is a
rotating rotor/nozzle 3 and is sealed to the end part of the
conduit 2 via a ring seal 4, which acts to prevent process fluid
being lost. A further seal 5 depicts another seal acts to prevent
dirt ingress in the clearance space between the rotor/nozzle 3 and
the hollow conduit 2. The rotor/nozzle 3 in this preferred
embodiment is supported for rotating movement on a screw thread 6
by means of a nut 7 held within the rotor/nozzle 3 on its axis of
rotation. The filter element 1 receives incoming fluid 8 and
provides filtered fluid 9. During filtration, filtered material
will build up on the inner surface of the filter element 1. The
cleaning head is used in a backwashing process as described below
in order to clean the filter element 1 and take filtered material
and backwashed fluid 10 away from the filter element 1, as shown in
cross-section, the hollow conduit 2 appears to be blocked in this
embodiment but in fact the central part including screw thread 6 is
supported by a number of arms or spokes (two of which are shown in
cross-section) that extend outwards from the central part to the
outer diameter. Spaces between these spokes form an open pathway
that allows fluid to flow past this support.
[0083] FIGS. 1c and 1d illustrate an alternative embodiment of the
filter cleaning head and its various components. As with the
embodiment described above, the filter cleaning head element in
FIGS. 1c and 1d is applied to a semi-permeable filter element wall
1, which in the preferred embodiment is a metal weave-wire sintered
screen. A hollow conduit 2 connects a part which acts as a nut 7
which in turn connects a combined rotor/nozzle 3 to the remainder
of the backwashing mechanism and also acts to support the
rotor/nozzle 3. Hence, in this embodiment the fixed part of the
mechanism is the nut 7 formed on the conduit 2, whereas in the
embodiment of FIGS. 1a and 1b the fixed part of the mechanism was a
threaded shaft 6 formed on the conduit 2. It will be appreciated
that other arrangements for the nut 7 and threaded shaft 6 are also
possible.
[0084] The rotating rotor/nozzle 3 in the embodiment of FIGS. 1c
and 1d is sealed to the nut 7 via a ring seal 4, which acts to
prevent process fluid being lost and prevent dirt ingress. The nut
7 is in turn sealed to the conduit 2 via a further seal 5 which
acts to prevent dirt ingress and process fluid entering into the
small clearance gap between the nut 7 and the hollow conduit 2 and
also holds the nut 7 snugly onto the conduit 2. A further simple
fastening such as grub screw (not shown) may be utilised to prevent
nut 7 rotating. Alternatively, nut 7 may be glued onto the end of
conduit 2, or joined by a threaded connection. In those
alternatives the seal 4 is not required.
[0085] The rotor/nozzle 3 in this preferred embodiment is supported
for rotating movement on a screw thread 6, the male part of which
is an integrated feature of the rotor/nozzle 3 and the female part
of which is an integrated feature of nut 7. The screw thread 6
maintains the rotor/nozzle 3 on its axis of rotation.
[0086] As with the first embodiment, the filter element 1 receives
incoming fluid 8 and provides filtered fluid 9. During filtration,
filtered material will build up on the inner surface of the filter
element 1. The cleaning head is used in a backwashing process as
described below in order to clean the filter element 1 and take
filtered material and backwashed fluid 10 away from the filter
element 1. In use the filter cleaning heads discussed above each
functions in a generally similar way as follows. The rotor/nozzle 3
is initially at a fully retracted position as shown in FIG. 1a or
FIG. 1c, and is activated when the backwashing process is
initiated. The backwashing process is initiated by the creation of
a pressure differential between the fluid 8 on the inside of the
filter element 1 and the fluid 10 in the vicinity of the backwash
outlet that occurs when a control valve at the backwash outlet is
opened (or a vacuum or suction apparatus is applied). At this
point, the backwashing fluid begins to move from the inside of the
filter element 8 to the backwash outlet.
[0087] Once the backwash flow begins to move, the fluid flow
kinetic energy contained in the backwash flow is converted into a
torque that rotates the rotor/nozzle 3. The design of the
rotor/nozzle 3 in the preferred embodiment includes rotor blades
formed as conic helixes which are particularly effective in
generating this torque. The conic helix shape of the rotor blades
is discussed in more detail below with reference to FIGS. 6 to
12.
[0088] The torque from the rotor/nozzle 3 and the consequent
rotation thereof is converted into a linear motion of the
rotor/nozzle 3 relative to the conduit 2 by the screw thread 6 and
nut 7. The rotating rotor/nozzle 3 moves from the retracted
position shown in FIG. 13 or FIG. 1c to a deployed position with
the end of the rotor/nozzle 3 in contact with the filter element 1
as shown in FIG. 1b or FIG. 1d. With the rotor/nozzle 3 in contact
with the filter element 1 the backwash flow is propelled by a
pressure difference between the fluid 9 downstream of the filter
element 1 and the fluid 10 in the conduit 2. When the motion of the
rotor/nozzle 3 is restrained by the inner wall of the filter
element 1 the torque applied to the rotor blades of the
rotor/nozzle 3 acts to create a sealing force that holds the end of
the rotor/nozzle 3 against the surface of the sealing element. This
sealing force promotes a very effective seal and prevents process
fluid from leaking between the inner of the filter element 8 and
the sealing face of the rotor/nozzle 3 and into the vicinity of the
backwash outlet 10.
[0089] The accumulated debris on the filter element wall 1 is thus
removed from the filter element wall by means of the backwash or
reverse flow of process fluid. In normal operation the pressure on
the inside of the filter element is greater than that on the
outside thereby creating a forward flow of fluid. By enabling a
second pressure differential between the outside of the filter
element and the inlet to the filter cleaning head forming part of
the backwash mechanism a high speed localised (isolated) reverse or
back-flow of process fluid is created, causing accreted filter
residue to be stripped from the filtration wall 1 and collected by
the filter cleaning head. The stripping of debris from the
filtration wall 1 is facilitated by the substantial shearing forces
created by the high speed backwash flow which in turn are generated
by the pressure differential across the filter element wall 1.
[0090] The sealing force generated by the rotor/nozzle 3 is
selected carefully so as to provide an effective seal between the
rotor/nozzle 3 and the inner wall of the filter element 1 whilst
avoiding such a high force that deformation of the filter element
wall may occur, or that the rotor/nozzle 3 may become stuck against
the filter element 1 and is not able to be reversed by an opposing
force that might be experienced in normal operation of the
backwashing mechanism. Such an opposing force can be usefully
applied if the manufacturing tolerance of the filter element 1
requires the rotor/nozzle 3 to `back off` or a short distance so as
to accommodate small differences in dimensions of the filter
element 1. Providing the sealing force is selected carefully, an
opposing force is able to cause a reverse rotation of the
rotor/nozzle 3 thus minimising the chance of seizure or damage to
the filter element 1. Once the variation in manufacturing tolerance
has passed the rotor/nozzle 3 may advance in its normal way towards
the filter element wall 1.
[0091] When the rotor/nozzle 3 is located at the deployed position
shown in FIG. 1b or FIG. 1d then the flow of backwash fluid begins
in the outer region 9, passes through the semi permeable filtration
wall 1 and hence causes a high speed localised (isolated) reverse
or back-flow of process fluid and dislodged debris to move into the
rotor/nozzle 3 of the filter cleaning head. This fluid and debris
flows along the hollow conduit 2 into the remainder of the
backwashing mechanism. The fluid 10 is then discharged to a
backwash outlet. In many filtration processes the backwash fluid is
a waste product and hence is discarded.
[0092] The high speed localised backwash flow generated at the
rotor/nozzle 3 causes cleaning of the filter as debris is stripped
from the filtration wall 1 and is collected by the filter cleaning
head. The stripping of debris from the filtration wall 1 is
facilitated by the substantial shearing forces created by the high
speed backwash flow.
[0093] FIG. 2 shows a filter cleaning head that is designed to be
retro-fitted onto an existing backwashing mechanism. The hollow
conduit 2 may fit over the end of an existing tube 11 protruding
from the existing backwashing mechanism and be sealed by a ring
seal 12 which holds the conduit 2 on the end of the tube 11 and
seals the joint. The tube 11 may be a part of a multi-head filter
cleaning device similar to that shown in FIGS. 4 and 5.
[0094] With this design the filter cleaning head can be used to
replace conventional filter cleaning heads employing nozzles such
as the spring loaded nozzles of WO 2006/008729 or the bellows type
nozzles of WO 2011/058556. As the nozzles of the cleaning heads
suffer from wear they are a consumable part and can be replaced
during maintenance. Replacing a conventional cleaning head with a
cleaning head using a rotor/nozzle 3 as described herein can result
in improved performance and can increase the time before the
nozzles need replacing again, for the reasons set out above.
[0095] FIGS. 3a and 3b show a design for the hollow conduit 2 that
provides a modular arrangement for a multi-head filter cleaning
device for a cylindrical filter element 1. With this design the
conduit 2 takes the form of a T-piece with a main flow passage
intended to align with the axis of the cylindrical filter element 1
and a branch passage that joins the rotor/nozzle 3, which is as in
FIG. 1, to the main flow path. The conduit 2 forms a segment of a
multi-head system and can be fitted together with other similar
conduits 2.
[0096] It will be appreciated that whilst FIG. 2 and FIG. 3a show a
cleaning head with features as described above in relation to FIGS.
1a and 1b this is a matter of convenience and the cleaning head
could instead have features as described above in relation to FIGS.
1c and 1d.
[0097] FIG. 3b shows two conduits 2 fitted within a cylindrical
filter element 1. The filter element 1 is shown in cross-section.
The joint between the conduits is designed for a `snap fit` and a
further ring seal 13 is included to seal adjacent segments
together. With this arrangement it is possible to build up
multiple-heads in a cleaning device for various lengths of filter
element 1 as required.
[0098] In order to effectively clean the internal surface of the
cylindrical filter element 1 the rotor/nozzle 3 of each cleaning
head should be placed close to the inner surface of the filter
element 1 when they are in the retracted position, so that a small
rotational movement will place the rotor/nozzle 3 of each cleaning
head in contact with the filter surface for effective cleaning.
Thus, the lengths of the side branches of the conduits 2 should be
set based on the radius of the filter element 1.
[0099] FIG. 4 shows the entire backwashing mechanism installed in a
filter arrangement that contains a single filter element. Parts of
the filter are shown in cross-section so that the backwashing
mechanism can be seen. The filter has a generally cylindrical
construction, with a filter element 1 that is cylindrical. A filter
body 14 encloses the filter element 1 and has an inlet 15 and an
outlet 16 and support brackets 17 and 18 that hold the filter
element 1 in place. The backwashing mechanism includes multiple
cleaning heads that are `snapped` together as described above in
relation to FIGS. 3a and 3b. Each cleaning head comprises a hollow
conduit 2, a rotor/nozzle 3 and other components as discussed above
in relation to FIGS. 1a and 1b. At one of the backwashing mechanism
is an outlet end piece 19 that allows fluid connection to the
remainder of the backwashing mechanism for the backwashed fluid 10
and also connects the main flow path of the hollow conduits 2 to a
shaft and motor/gearbox 22 via a bearing. The bearing permits
rotational movement and longitudinal movement of the backwashing
mechanism. At the other end of the backwashing mechanism a blind
end piece 20 provides a closed end and connects to a similar
bearing so that the backwashing mechanism is held for rotational
movement between the two ends 19, 20 and can also slide along the
length of the cylindrical filter element 1. A mounting flange 21
supports the shaft and motor/gearbox 22, which provides the driving
mechanism.
[0100] The driving mechanism provided by the shaft and
motor/gearbox 22 can rotate the backwashing mechanism whilst
simultaneously moving the backwashing mechanism in a linear motion
along the axis of the filter element 1. Movement may be by means of
an electric motor and screw or other electro-mechanical, pneumatic
or hydraulic arrangement. As the backwashing mechanism is
simultaneously rotated and moved linearly, the filter cleaning
heads forming part of the backwashing mechanism follow a helical
trajectory. Thus, the filter cleaning heads are able to be conveyed
over 100% of the entire inner surface of the filter element 1 such
that debris can be collected from all parts of the semi-permeable
filtration wall. Thus, the entire surface of the semi-permeable
filtration wall can be cleaned of debris.
[0101] In use, the filter receives fluid via inlet 15 and passes
this fluid 8 to the inside of the cylindrical filter element 1.
Filtered fluid 9 is expelled via the outlet 16. When it is
necessary to clean the filter, for example when a pressure loss
across the filter element 1 has increased beyond a threshold level,
the backwashing mechanism is activated. This can be done by a valve
24 or similar control mechanism. This results in a pressure
differential between the fluid 8, 9 undergoing filtration and the
backwash fluid 10. Fluid therefore flows along the rotor/nozzles 3
resulting in torque that seals the rotor/nozzles 3 against the
filter wall as discussed above. Fluid 9 from the outer region of
the filter then flows back through the semi permeable filtration
wall 1 causing a high speed localised (isolated) reverse or
back-flow of process fluid at open end of the rotor/nozzles 3. This
results in process fluid and debris moving into the rotor/nozzles 3
of the filter cleaning head, along the hollow conduits 2 to the
main flow path of the backwashing mechanism and finally to the
backwash outlet region 10. The filter body 14 includes a backwash
outlet 23 on which may be installed a suitable control valve 24
and/or a vacuum or suction apparatus 25 that enables the pressure
differential causing the backwash process to be initiated.
[0102] FIG. 5 illustrates an example of multiple backwashing
mechanisms installed in a filter arrangement that contains a
plurality of cylindrical filter elements 1. The filter body 14 has
an inlet 15 and an outlet 16 and supports 17 and 18 that hold the
plurality of filter elements 1 in place. Liquid passes through the
filter elements 1 in parallel. In this embodiment, the multiple
backwashing mechanisms each include multiple filter cleaning heads
that are `snapped` together as described above. Each filter
cleaning head includes a hollow conduit 2 and a rotor/nozzle 3 as
well as other components as discussed above. The ends of the
backwashing mechanisms include end pieces 19 and 20 as described
above in relation to FIG. 4, with connections to shafts and
motor/gearboxes 22 that provide suitable drive mechanisms.
[0103] The drive mechanisms provided by the shafts and
motor/gearboxes 22 are arranged to rotate the individual
backwashing mechanisms whilst simultaneously moving the individual
backwashing mechanisms in a linear motion along the axis of the
individual filter elements 1. As for the arrangement of FIG. 4,
movement may be by means of an electric motor and screw or other
electro-mechanical, pneumatic or hydraulic arrangement.
[0104] In use, the backwash fluid passes through the filter wall 1
into the rotor/nozzles 3 and cleans the filter residue in the
manner described above. The filter of FIG. 5 has a single backwash
outlet 23 for all of the parallel filter elements 1. This outlet 23
includes a suitable control valve 24 and/or a vacuum or suction
apparatus 25 that enables the pressure differential causing the
backwash process to be initiated for all of the parallel filter
elements at once.
[0105] In an alternative embodiment, which is not shown, each of
the filter elements is provided with a separate outlet or a valve
system to permit the separate filter elements to be cleaned
independently. This may be useful in systems where the build-up of
residue occurs at different rates for the different parallel filter
elements.
[0106] FIGS. 6a and 6b depict an embodiment of a rotor for the
combination rotor/nozzle 3 including an outer peripheral rim 30,
blades 31 and inner peripheral surface 32. As explained above, the
rotor is used to turn the flow of a liquid and the pressure
differential during backwashing into rotational movement and torque
on the rotor/nozzle 3 to hold the cleaning head against the filter
wall 1. The rotor can be mounted to the cleaning device with a
screw thread arrangement using a nut held at the axis of rotation
of the rotor within body of the rotor inside of the inner
peripheral surface 32, hence being mounted as shown in FIGS. 1a, 1b
and 2 to 3b. The embodiment of FIGS. 1c and 1d could be used as an
alternative. The blades 31 extend between the inner peripheral
surface 32 and the outer rim 30 and hence form enclosed flow paths.
In this embodiment the underlying spiral that forms the shape of
the blades 31 is based upon an Archimedean spiral where there is a
linear increase in radius r with the polar coordinate .theta.. The
resulting rotor therefore has the shape of a frustum of a cone. As
noted below, other types of curve can be used. Three rotor blades
31 can be seen within the rotor and also the inner peripheral
surface 32. The longitudinal axis of the rotor 33 is shown by a
centre line. Throughout these figures, the maximum outer diameter
of the rotor is denoted by Do and the minimum outer diameter by do.
The length of the rotor is denoted by L and the local length l is
measured from the end of the rotor having the minimum outer
diameter do.
[0107] FIGS. 7a and 7b depict the rotor of FIGS. 6a and 6b with
outer peripheral rim 30 partially hidden for clarity. The inner
peripheral rim 32 is also highlighted. The three rotor blades 31
have a shape formed by a pair of conic helixes. Outer conic helix
34 is a helix formed on the internal surface of the outer rim 30
and forms a varying outer radius ro of the blade 31. Inner conic
helix 35 is a helix formed on the outside of the inner cone 32 and
forms a varying inner radius ri of the blade. Both of the helixes
have an increasing radius and a decreasing helical pitch along the
longitudinal axis 33. The blades 31 have a decreasing helical pitch
resulting from an increasing helical frequency. The pair of conic
helixes 34 and 35 are generated in a clockwise direction and have
different initial radii which increase at an equal rate to form a
pair of parallel conic helixes.
[0108] FIGS. 8a and 8b show perspective views of the rotor of FIGS.
6 and 7 in which further detail of the shape of the blades 31 can
be seen.
[0109] FIGS. 9a and 9b show a variation of the rotor design. In
this embodiment the pair of conic helixes 34 and 35 are generated
in a clockwise direction and form the shape of the blades 31 in the
manner discussed above. However, the radius ri of the inner conic
helix 35 increases at a lesser rate than the radius ro of the outer
conic helix 34 to thereby form a pair of non-parallel conic helixes
that are spaced further apart at the large diameter end of the
rotor than at the small diameter end of the rotor.
[0110] FIGS. 10a and 10b show a further variation in which the
radius ri of the inner conic helix 35 increases at a greater rate
than the radius ro of the outer conic helix 34 to thereby form a
pair of non-parallel conic helixes that are spaced closer together
at the large diameter end of the rotor than at the small diameter
end of the rotor.
[0111] FIGS. 11a and 11b show a further variation which has
parallel inner and outer cones as in FIGS. 6 and 7, but in which
the helical pitch decreases at a slower rate than the previously
described embodiments. This results in a slower rate of increase of
the helical frequency. FIGS. 12a and 12b show the opposite variant
in which the helical pitch decreases at a greater rate resulting in
a faster rate of increase of the helical frequency.
[0112] For the rotating rotor/nozzle 3 the design of the blades and
rotor can be optimised for expected operating conditions of the
filter, as discussed below with reference to FIGS. 13 to 15.
[0113] The geometry of the rotor facilitates the conversion of the
kinetic energy in the liquid fluid flow to rotational force or
torque. The geometry of the rotor is based on pair of conic helixes
34, 35 that have an increase in radius r with a polar coordinate
.theta. along the longitudinal axis 33, each helix 34, 35
possessing a different initial radius. The pair of conic helixes
34, 35 also have a pitch that decreases with the polar coordinate
.theta. as the radius increases. The decreasing helical pitch
provides an increasing helical frequency. This type of conic helix
may be defined as a three dimensional spiral having varying radius
r as a function of the polar coordinate .theta. but also having a
third variable, the length l, varying also as function of the polar
coordinate .theta..
[0114] The pair of conic helixes may be generated in a clockwise or
anticlockwise direction and as shown in FIGS. 11A to 12B the rate
of decrease of the helical pitch resulting in an increase in
helical frequency may be varied to obtain an optimum decrease of
helical pitch per unit of length. Other variables that have a
direct effect on the torque produced are the initial and final
radii of the pair of conic helixes (and thus the minimum and
maximum inner and outer diameters of the rotor) and the overall
length of the rotor. These may also be optimised for a given flow
situation.
[0115] The rotor blade surfaces of the rotor are formed when the
pair of conic helixes are connected together in the radial
direction. In the rotor shown in the Figures three identical rotor
blades 31 are present. There could alternatively be less or more
identical rotor blades 31 spaced equally around the rotor. The
rotor blades 31 extend between the inner peripheral surface 32 and
the outer rim 30 and are fixed to both of the inner peripheral
surface 32 and the outer rim 30 for rotation therewith.
[0116] A hydrodynamic reaction force is created on a solid surface
when a body of fluid flowing over the solid surface experiences a
change of momentum. The net hydrodynamic force acting on the body
of fluid in a particular direction is equal to the rate of change
of momentum of the body of fluid in that direction as dictated by
Newton's Second law. In accordance with Newton's Third Law, an
equal and opposite hydrodynamic reaction force acts on the solid
surface bounding the body of fluid. Examples of such hydrodynamic
reaction forces are those found when a jet of water strikes a wall,
or the force felt in a pipe system when the fluid is forced to turn
a bend or the force felt on a solid body when placed in a flowing
fluid forcing the fluid to flow around it.
[0117] In the rotor described herein a solid surface bounding the
body of flowing fluid is formed by the front and rear of a pair of
rotor blades and the inner and outer rims of the rotor. As the body
of fluid flows through the specially shaped rotor and its
complicated flow passages it is constantly forced to change
direction due to the shape of the blades and the decreasing helical
pitch from inlet to outlet which results in an increasing helical
frequency, thereby resulting in a continuous rate of change of
momentum. This rate of change of momentum necessarily results in a
hydrodynamic reaction force that acts on the solid surfaces of the
rotor. As the conic helix has a given geometrical direction, this
being clockwise or anticlockwise, the hydrodynamic reaction force
acts in the opposite direction and since the centre of the
hydrodynamic reaction force is displaced at a radial distance from
the longitudinal axis, a torsional force is generated that acts
around the longitudinal axis of the rotor.
[0118] The underlying mathematical spiral of the conic helix can be
based on Archimedean, Euler, Fibonacci, Hyperbolic, Lituus,
Logarithmic, Theodorus or any other known spiral having varying
radius r as a function of the polar coordinate .theta. but also
having a third variable, the length l, varying also as function of
the polar coordinate .theta.. For the reasons discussed above, it
is apparent that an underlying spiral possessing a more rapid
change in inner and outer radius r with the polar coordinate
.theta. would induce a more rapid rate of change of momentum
necessarily resulting in an increased hydrodynamic reaction force.
This is akin to comparing a shallow bend with a sharp bend. It is
well known that the force felt in a pipe system is increased when
the fluid is forced to turn the sharper of the two bends.
[0119] In the embodiments described above, for reasons of
simplicity, the underlying spiral is based upon an Archimedean
spiral when there is a linear increase in radius r with the polar
coordinate .theta.. However, it is equally feasible to construct
the rotor by way of a non-linear increase in inner and outer radii
r with the polar coordinate .theta. through the use of a different
underlying mathematical spiral such as Archimedean, Euler,
Fibonacci, Hyperbolic, Lituus, Logarithmic, Theodorus or any other
known spiral having varying radius r as a function of the polar
coordinate .theta. but also having a third variable, the length l,
varying also as function of the polar coordinate .theta.. The use
of an Archimedean spiral with linear increase in the radii r with
the polar coordinate .theta. provides a conic helix formed about a
straight sided frustocone as shown in the Figures. Conversely, a
non-linear increase in the inner and outer radii r with the polar
coordinate .theta. would provide a different shape, for example the
external and internal conic surfaces may be curved.
[0120] In the preferred embodiments illustrated herein, the pair of
conic helixes are chosen to have a linear increase in radii r with
the polar coordinate .theta. along the longitudinal axis, each
possessing a different initial radius. In some embodiments, as in
FIGS. 9a to 10b the increasing radius of either conic helix may
increase at greater or lesser rates to form a pair of non-parallel
conic helixes. In other embodiments, as in FIGS. 118 to 12b they
may increase at the same rate to form a pair of parallel conic
helixes. Simultaneously, the helical pitch is also decreased by way
of varying l as a function of .theta. continuously or in discrete
steps along the longitudinal axis 33. The rate of decrease of
helical pitch or the rate of increase of helical frequency in these
embodiments is linear. It may alternatively be non-linear.
[0121] The helix shape, radius increase and pitch decrease combine
to provide the overall hydrodynamic reaction force on the rotor and
thus the torque required to rotate the nozzle and press it against
the filter wall. These parameters may be optimised to maximise the
power extraction from a given fluid flow or to limit the power
extraction from a given fluid flow if required. The following set
of equations considers the hydrodynamic reaction forces and torques
generated.
{dot over (m)}.sub.in={dot over (m)}.sub.out={dot over (m)} 1
F.sub.x={dot over (m)}(u.sub.2-u.sub.1) [2.1]
F.sub.y={dot over (m)}(v.sub.2-v.sub.1) [2.2]
F.sub.g={dot over (m)}(w.sub.2-w.sub.1) [2.3]
T.sub.x=F.sub.g.times.y-F.sub.y.times.z [3.1]
T.sub.y=F.sub.x.times.z-F.sub.g.times.x [3.2]
T.sub.g=F.sub.y.times.x-F.sub.x.times.y [3.3]
[0122] As stated in Equation 1, the mass flow {dot over (m)} into
the rotor is constant. The hydrodynamic reaction forces F.sub.x,
F.sub.y and F.sub.g are necessarily produced due to the
continuously decreasing helical pitch or in other words, due to a
continuous change in the direction of the fluid flow and thus a
change in the velocity components u, v and w of the fluid between
the velocity components at first and second arbitrary cross
sections in the rotor, the first and second arbitrary cross
sections being at different distances along the rotor length. This
results in a rate of change of momentum and the hydrodynamic
reaction forces as expressed by Equation [2.1] to [2.3]. Observing
the right hand rule, the torques T.sub.x, T.sub.y and T.sub.g
around the x, y and z axis of the rotor are produced by the out of
balance cross product of the hydrodynamic force components and the
relevant distances x, y and z from the longitudinal axis about
which they act as shown by Equations [3.1] to [3.3].
[0123] According to this set of equations it can be understood that
a change in the rate of decrease of the helical pitch will result
in an increase or decrease in the torsional forces and power
output. A decrease in torsional force is achieved by a slower rate
of decrease of helical pitch and an increase in torsional force is
achieved by a faster rate of decrease of helical pitch.
[0124] The distance from the longitudinal axis at which the
hydrodynamic reaction forces act is continuously increased or
decreased by the change in radius of the pair of conic helixes. For
each complicated flow passage a separate set of torsional forces
result, the total torsional force around the longitudinal axis of
the rotor being the sum of all torsional forces acting around the
longitudinal axis of the rotor.
[0125] In the case where the increasing radii of the pair of conic
helixes increase at the same rate to form a pair of parallel conic
helixes this results in an equal increase in the distance from the
longitudinal axis at which the hydrodynamic reaction forces act and
thus a magnification of the torsional force and power output as
determined by Equation [3.1] to [3.3]. In this case, the cross
sectional areas at first and second arbitrary cross sections in the
rotor increase at a constant rate and since the mass flow is
constant, the velocity differences and thus hydrodynamic reaction
forces produced are constant. The magnification of the torsional
force and power output is only dependent on the rate at which the
radius of the pair of conic helixes increases.
[0126] Where the radius of the pair of conic helixes increase at
greater or lesser rates to form a pair of non-parallel conic
helixes, this has the effect of changing the rate at which the
cross sectional areas at first and second arbitrary cross sections
in the rotor increase. When the inner conic helix increases in
radius at a slower rate than the increase in radius of the outer
conic helix, the arbitrary cross sectional areas increase at a
faster rate. This has the effect of reducing the changes in the
velocity components and since the mass flow is constant, the
hydrodynamic reaction forces produced are lower. When the inner
conic helix radius increases at a faster rate than the outer conic
helix radius, the arbitrary cross sectional areas increase at a
slower rate. This has the effect of increasing the changes in the
velocity components and since the mass flow is constant, the
hydrodynamic reaction forces produced are larger. Thus, through
manipulation of the parameters of the rotor, it is possible to
manipulate the extracted power output and optimise or restrict it
as required.
[0127] In addition, the connection between the pair of conic
helixes is not limited to being straight. The connection may be
curved, for example, a concave surface may be used to increase the
surface area along the surface of the specially shaped rotor blade
in order to spread the resulting hydrodynamic forces over a larger
area and reduce internal stresses. Similarly, the pair of conic
helixes are generally axially aligned for simplicity but may be
slightly misaligned in order to change the surface characteristics
of the conic helixes in a beneficial way.
[0128] As discussed above, various parameters of the rotor and
blade shape can be varied depending on the purpose of the rotor and
the operating conditions that it will be exposed to, such as flow
rate and so on. FIGS. 13 to 15 illustrate how changes to these
parameters affect the performance of the rotor.
[0129] FIG. 13 is a graph illustrating the effect of varying the
ratio of the outer maximum diameter Do of the rotor to the minimum
outer diameter do. In this case, the radii of the pair of conic
helixes are increased at the same rate to form a pair of parallel
conic helixes. The increasing diameter results in an increase in
the distance from the longitudinal axis at which the hydrodynamic
reaction forces act and thus provides a magnification of the
torsional force. The magnification of the torsional force is
dependent on the rate at which the radii of the pair of conic
helixes increase.
[0130] As a baseline. FIG. 13 uses an arrangement with no change in
diameter, i.e. where the ratio of maximum and minimum radii [Do/do]
is one. This is a rotor where the radii of the pair of conic
helixes does not increase i.e. this is a rotor based upon a
cylindrical helix and not a conic helix. The rotor described
herein, which are based on blades formed by conic helixes, have a
ratio of greater than one and this provides a torque multiplication
and an increase in efficiency as shown in the Figure.
[0131] In some of the variants discussed above, the inner and outer
conic helixes are formed on non-parallel conic surfaces. FIG. 14 is
a graph illustrating the effect of increasing or decreasing the
relative radii of the pair of conic helixes to form a pair of
non-parallel conic helixes. When the inner conic helix increases in
radius at a slower rate than the increase in radius of the outer
conic helix (i.e. [.DELTA.ri/L]/[.DELTA.ro/L]<1), arbitrary
cross sectional areas at first and second longitudinal distances
along the rotor increase at a faster rate. This has the effect of
reducing the changes in the velocity components and since the mass
flow is constant, the hydrodynamic reaction forces and torsional
forces produced are lower. When the inner conic helix radius
increases at a faster rate than the outer conic helix radius (i.e.
[.DELTA.ri/L]/[.DELTA.ro/L]>1), the arbitrary cross sectional
areas within the rotor increase at a slower rate. This has the
effect of increasing the changes in the velocity components and
since the mass flow is constant, the hydrodynamic reaction forces
and the torsional forces produced are larger. The point where
[.DELTA.ri/L]/[.DELTA.ro/L]=1 is a rotor where the radii of the
pair of conic helixes increase at the same rate to form a pair of
parallel conic helixes.
[0132] Other variants discussed above involve the use of different
changes in pitch for the decreasing pitch of the conic helixes.
FIG. 15 is a graph illustrating the effect of changes in the rate
of decrease of the helical pitch that results in a change in the
rate of increase of helical frequency .DELTA.f. As shown in the
Figure, a change of this nature will result in an increase or
decrease in the torsional forces and thus power output. A decrease
in torsional force is achieved by a slower rate of decrease of
helical pitch or a slower rate of increase of helical frequency and
an increase in torsional force is achieved by a faster rate of
decrease of helical pitch or a faster rate of increase in helical
frequency. In FIG. 15, the rotor labelled .DELTA.f=0:1 is based
upon the rotor presented in FIGS. 6a to 8b. In comparison, the
rotor labelled .DELTA.f=0.05 is based upon the rotor presented in
FIGS. 11a and 11b whilst the rotor labelled .DELTA.f=0.25 is based
upon the rotor presented in FIGS. 12a and 12b.
[0133] The relationships set out in FIGS. 13 to 15 enable
optimisation of the rotor design depending on the filter
characteristics. For low pressure filtration, the pressure
differential would typically be lower and so would generate a low
backwash flow rate. For a low backwash flow rate the rotor should
have parameters selected from the right hand side of the graphs of
FIGS. 13 to 15. Rotors with these parameters will produce larger
forces for a given flow. Conversely, for high pressure filtration,
the pressure differential would generally by higher and would
generate a high backwash flow rate. The rotor for higher pressure
differential should have parameters selected from towards the left
hand side of the graphs as these rotors will produce smaller forces
for a given flow. The rotor design and the pressure differential
should be matched with the sealing forces required for good contact
with the filter element wall whilst also ensuring the sealing force
is not too high to damage the filter screen.
[0134] It will be appreciated that the cleaning head described
above can be used for any filter arrangement and is not limited to
the cylindrical filter element and rotating backwash arrangement
described above. In the preferred embodiments above the fluid is
moving from the inside to the outside of the cylindrical filter
element 1 but the reverse direction may also be accommodated.
Alternative systems may be used to traverse the cleaning head
across the filter wall, as appropriate for the geometry of the
filter wall. The cleaning head may be adapted for retro-fitting to
any suitable known backwashing mechanism, for example by design of
the conduit 2 to join with flow passages of the known backwashing
mechanism in an appropriate fashion.
* * * * *